Cook lasagne sheets in a large saucepan of boiling water for 2-3 mins or until just tender. Transfer to a bowl of cold water.
Preheat oven to 180˚C. Cut down either side of silverbeet stems and remove white stalks. Discard stems and stalks. Wash leaves and, without drying, roughly tear. Place in a large saucepan. Cook over medium-low heat, covered, shaking the pan and turning silverbeet occasionally, for 2-3 mins or until wilted. Set aside for 5 mins to cool slightly. Squeeze to remove excess liquid. Finely chop.
Heat oil in a medium frying pan over medium heat. Add the onion and garlic and cook, stirring, for 5 mins or until onion softens. Add the prosciutto and cook, stirring, for 5 mins or until golden.
Combine silverbeet, onion mixture, ricotta, parmesan and pine nuts in a large bowl. Season with salt and pepper.
Place 1 lasagne sheet on a clean work surface. Spoon one-tenth of the ricotta mixture over the lasagne sheet. Starting from 1 short end, roll up to enclose filling. Repeat with remaining lasagne sheets and filling. Use a serrated knife to cut each pasta roll into 2 pieces.
Combine the tomato and pasta sauce in a bowl and spoon into the base of a 25cm-diameter baking dish. Place pasta rolls, cut-side up, side by side, over the sauce. Sprinkle with the pizza cheese. Bake for 30 mins or until golden and heated through. Sprinkle with parsley leaves and serve with mixed salad leaves.